The present invention concerns communications between the stations of a distributed type network.
The network is for example a local wireless network, the stations of which communicate with one another by sharing a radio channel.
A distributed type network does not have a base station to manage the communications between the stations.
In a first aspect, the invention concerns the broadcasting of messages in the network.
According to a known broadcasting mechanism used in a MAC (Medium Access Control) access protocol for a local wireless network of the distributed type, each station in the network rebroadcasts the messages which it receives.
The messages have for example a limited life, which can be expressed by a maximum number of rebroadcasts. As long as a message has not reached its maximum rebroadcasting number, it is rebroadcast.
The rebroadcasting of messages means that a station may receive duplicated messages, that is to say those containing the same useful data, from several different stations. The station under consideration will rebroadcast each of these messages. In other words, the station under consideration receives the xe2x80x9csamexe2x80x9d message several times, and rebroadcasts it on each occasion. The duplicated data are then sorted and eliminated by layers on top of the MAC layer. This system generates a great deal of traffic and therefore a high occupation of the radio channel, to the detriment of new data messages. In addition, this increases the risk of collision of messages and consequently the risk of the loss of a message.
In order to improve message broadcasting, it is possible to select a sub-set of stations which are distributed through the network which alone will be authorized to rebroadcast the messages received in a broadcast. The number of rebroadcasts is thus limited. However, a station always rebroadcasts a message at least once. In addition, it is possible for it to rebroadcast the xe2x80x9csamexe2x80x9d message several times.
In a second aspect, the invention concerns the routing of messages in the network.
A routing function makes communications possible between the stations of the network, by determining the communication paths in the network. This function is adapted to the constraints of a local wireless network, notably the limited passband, and the mobility of the stations or alterations in the station environment which produce changes in the network topology.
Known routing methods are based on periodic exchanges of routing messages in order to detect changes in network topology. The routing function must modify the communication paths in the network as quickly as possible, so that the known paths correspond to the actual paths existing in the network, otherwise the risk of faulty routing and loss of messages is great. It is therefore necessary for the routing messages to be frequent.
However, the routing messages occupy the radio channel, to the detriment of useful data. The routing function must therefore generate as few routing messages as possible, in order to occupy little passband.
These constraints are conflicting and make the operation of the routing function complex.
The present invention aims to remedy the drawbacks of the prior art by providing a method enhancing communications between the stations of a distributed network.
Firstly, the invention provides a message broadcasting method which monitors the messages at the MAC layer, before rebroadcasting them.
For this purpose, the invention proposes a method of broadcasting messages between stations in a network, each station having in memory a respective first table containing identifiers of final destination stations of messages associated with identifiers of intermediate destination stations of messages, characterised in that any station under consideration performs the following operations when it receives a message:
storing in a second table data relating to the said message and including at least one message identifier and an identifier of a station sending the said message,
comparing the message identifier with the message identifiers previously stored in the second table,
seeking in the first table of the station under consideration a group of stations which are both a final destination station and an intermediate destination station, and
broadcasting a second message if and only if the identifier of the said message is different from the identifiers previously stored in the second table and if the said group includes at least one station different from the station which sent the said message.
The method according to the invention resolves the problem stated above, by using data traffic at the MAC (Medium Access Control) level. The invention uses on the one hand the data messages transported in the network and on the other hand the station routing table, in order to determine whether a message is to be rebroadcast. Message rebroadcastings are less numerous, which reduces the risk of collision and therefore of message loss.
The broadcast data can be user data or routing information, for example.
According to a preferred characteristic, the second message has a message identifier which is that of the said message and an intermediate sending station address which is that of the station under consideration. The broadcasting of the second message is equivalent to the rebroadcasting of the message currently being processed.
According to another preferred characteristic, the message identifier includes the address of the initial sending station of the first of a set of previous messages having the same message identifier as the said message. The messages are thus identified simply and reliably.
Correlatively, the invention concerns a communication station in a network, having in memory a respective first table containing identifiers of final destination stations of messages associated with identifiers of intermediate destination stations of messages, characterised in that it has, or in that it is adapted to cooperate with:
means of storing in a second table data relating to a message which it receives and including at least one message identifier and an identifier of a station sending the said message,
means of comparing the message identifier with the message identifiers previously stored in the second table,
means of seeking in the first table of the station under consideration a group of stations which are both a final destination station and an intermediate destination station, and
means of broadcasting a second message if and only if the identifier of the said message is different from the identifiers previously stored in the second table and if the said group includes at least one station different from the station which sent the said message.
The communication station according to the invention has the same advantages as those of the method described previously.
Secondly, the invention provides a method of detecting paths and transmitting routing information in a distributed network, which makes it possible to detect the rupture of a link and to transmit the corresponding information, rapidly and independently of the execution of the routing algorithm.
To this end, the invention proposes a method of routing messages between stations in a network, each station having in memory a respective first table containing identifiers of final destination stations of messages respectively associated with identifiers of intermediate destination stations of messages, characterised in that any station under consideration performs the following operations when it receives a data message:
storage, in a respective second table, of data concerning the message and including at least one message identifier, an intermediate sending station identifier, an intermediate destination station identifier, a final destination station identifier and a message retransmission number,
and, if the message retransmission number reaches a predetermined value, if the station under consideration is not the intermediate destination station and if the station under consideration has in its first table the final destination station identifier associated with an intermediate destination station identifier different from that of the intermediate sending station,
sending of a specific routing message intended for the intermediate sending station in order to indicate to it the existence of a path between the station under consideration and the final destination station.
The method according to the invention resolves the problem stated above, by using the data messages transported in the network in order to deduce that there is the rupture of a link between two stations, in order to transmit an item of routing information to the station which has suffered the link rupture, or to a set of stations.
The method makes it possible to modify the routing tables of the stations in the network very quickly, independently of the periodicity of the execution of the routing algorithm.
By virtue of the method according to the invention, the mobile stations are aware of the changes to the paths in the network. By taking account of these modifications in order to modify the station routing tables, the number of messages lost is considerably reduced. The routing of the communications is thus made more reliable.
The method adapts to any known routing function, whose execution is independent of the method according to the invention. By virtue of the reliability obtained by the invention, the routing algorithm can be executed with a greater period, and consequently generate fewer routing messages. The increase in routing traffic due to the specific routing messages according to the invention is thus negligible compared with the reduction in routing traffic due to the longer period of the routing algorithm.
The performance of the network is thus improved, it resists better the disturbances consisting of the link ruptures, and is therefore more robust overall.
According to preferred characteristics, the specific routing message includes as least the address of the station under consideration, the final destination station of the said message, and a transmission cost between the station under consideration and the final destination station of the said message, or the specific message contains up to the entire first table of the station under consideration.
These data make it possible to modify the routing table of the destination station of the specific routing message.
According to a preferred characteristic, the message identifier includes the address of the initial sending station of the first of a set of previous messages having the same message identifier as the said message. The messages are thus identified simply and reliably.
In another aspect, the invention proposes a method of routing messages between stations in a network, each station having in memory a respective first table containing identifiers of final destination stations of messages respectively associated with identifiers of intermediate destination stations of messages, characterised in that any station under consideration performs the following operations, when it receives a specific routing message indicating the existence of a path between two stations:
ascertaining whether the station under consideration is a destination of the specific routing message and, in the event of a positive response,
modifying the first table of the station under consideration according to the specific routing message.
The routing table is thus modified quickly and a new path can be used as from the next message to be routed.
The invention also concerns a communication station in a network, having a memory for storing a respective first table containing identifiers of final destination stations of messages respectively associated with identifiers of intermediate destination stations of messages, characterised in that it has, or in that it is adapted to cooperate with:
means of storing, in a respective second table, data concerning each data message which it receives, these data including at least one message identifier, an intermediate sending station identifier, an intermediate destination station identifier, a final destination station identifier and a message retransmission number,
means of checking that the message retransmission number reaches a predetermined value, that the station under consideration is not the intermediate destination station and that the station under consideration has in its first table the final destination station identifier associated with an intermediate destination station identifier which is different from that of the intermediate sending station,
means of sending a specific routing message destined for the intermediate sending station in order to indicate to it the existence of a path between the station under consideration and the final destination station.
In another aspect, the invention proposes a communication station in a network, having in memory a respective first table containing identifiers of final destination stations of messages respectively associated with identifiers of intermediate destination stations of messages, characterised in that it has, or in that it is adapted to cooperate with:
means of receiving a specific routing message indicating the existence of a path between two stations,
means of ascertaining whether the station under consideration is the destination of the specific routing message, and
means of modifying the first table of the station under consideration as a function of the specific routing message.
The communication station according to the invention has the same advantages as those of the method which were described previously.
The present invention also concerns a storage medium, such as a floppy disk or a CD-ROM.
The advantages of this storage medium are similar to those previously described.